Heterophase Systems

Some of the most difficult heterophase systems to characterize are those based on hydrocarbon polymers such as mbber-toughened polypropylene or other blends of mbbers and polyolefins. Eecause of its selectivity, RuO staining has been found to be usehil in these cases (221,222,230). Also, OsO staining of the amorphous blend components has been reported after sorption of double-bond-containing molecules such as 1,7-octadiene (231) or styrene (232). In these cases, the solvent is preferentially sorbed into the amorphous phase, and the reaction with OsO renders contrast between the phases. 

Analyzing the behavior of filled polymers, as any other heterophase systems, two aspects should be distinguished. First, these are the properties of such systems, i.e. their inherent characteristics, independent of a measuring method if, of course, the measurements are correct (to select criteria of correctness of an experiment, carried out with multiphase systems, seems to be an independent and by no means a simple problem). Second, this is a manifestation of these properties when heterophase systems flow in channels of different geometrical form. Behind all this stands the basic applied problem—finding out how the properties of filled polymers, appearing during their flow, affect the properties of finished articles. 

As has already been emphasized in Fig. 1.1, there is the further problem of connecting the mesoscopic scale, where one considers length scales from the size of effective monomers to the scale of the whole coils, to still much larger scales, to describe structures formed by multichain heterophase systems. Examples of such problems are polymer blends, where droplets of the minority phase exist on the background of the majority matrix, etc. The treatment of... 

ESRI methods have been developed in our Detroit laboratory for the study of heterophasic systems such as ABS [14,40,59,87-89] and HPEC [61,90], both containing bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate (Tinuvin 770) as the stabilizer, and exposed to thermal treatment and UV irradiation. The HAS-NO provided the contrast necessary in the imaging experiments. The major objectives were to examine polymer degradation under different conditions to assess the effect of rubber phase, polybutadiene (PB) in ABS and ethylene-propylene rubber (EPR) in HPEC, on the extent of degradation and to evaluate the extent of... 

The ESRI experiments described in our publications and summarized in this chapter led to spatially resolved information on the effect of treatment conditions, amount of stabilizer, and polymer composition on the degradation rate. In the heterophasic systems studied in our laboratory, ESRI has identified specific morphological domains where chemical processes are accelerated. The combination of ID and 2D spectral-spatial ESRI experiments led to mapping of the stabilizer consumption on two length scales within the sample depth on the scale of a few mm, and within morphological domains on the scale of a few gm. 

Considering theoretically a copolymerization on the surface of a miniemulsion droplet, one should necessarily be aware of the fact that this process proceeds in the heterophase reaction system characterized by several spatial and time scales. Among the first ones are sizes of an individual block and macromolecules of the multiblock copolymer, the radius of a droplet of the miniemulsion and the reactor size. Taking into account the pronounced distinction in these scales, it is convenient examining the macrokinetics of interphase copolymerization to resort to the system approach, generally employed for the mathematical modeling of chemical reactions in heterophase systems [73]. 

Absorbance subtraction can be considered as a spectroscopic separation technique for some problems in polymers. An interesting application in FT-IR difference spectroscopy is the spectral separation of a composite spectrum of a heterophase system. One such example is a semicrystalline polymer which may be viewed as a composite system containing an amorphous and crystalline phase53). In general, the infrared spectrum of each of these phases will be different because in the crystalline phase one particular rotational conformation will predominate whereas in the disordered amorphous regions a different rotamer will dominate. Since the infrared spectrum is sensitive to conformations of the backbone, the spectral contributions will be different if they can be isolated. The total absorbance A, at a frequency v of a semicrystalline polymer may be decomposed into the following contributions... 

In the case of the heterophase systems resulting from the ABA block polymers, the strength is reinforced because of the ability of the plastic,... 

These findings suggest strongly that the composition of the elastomeric molecule and the nature of the functional groups affect its compatibility and rate of reaction with the epoxy resin, which in turn affect the molecular and morphological structure of the heterophase system. These data indicate the importance of the acrylonitrile comonomer and the carboxyl groups in controlling the polarity of the rubber, and subsequently its compatibility characteristics with the epoxy. We could also... 

Given the preceding mechanistic discussion, one would not expect the reactivity ratios to represent true kinetic parameters. Indeed, the reactivity ratios are sensitive to monomer and simple electrolyte concentrations, comonomer feed compositions, temperature and whether the reaction was carried out in aqueous solutions or a heterophase system. Clearly the data from the various groups are partly inconsistent, but still some general conclusions regard DADMAC/AAM copolymerization, listed in Table 6, are reasonable. 

With the advent of advanced characterization techniques such as multiple detector liquid exclusion chromatography and - C Fourier transform nuclear magnetic resonance spectroscopy, the study of structure/property relationships in polymers has become technically feasible (l -(5). Understanding the relationship between structure and properties alone does not always allow for the solution of problems encountered in commercial polymer synthesis. Certain processes, of which emulsion polymerization is one, are controlled by variables which exert a large influence on polymer infrastructure (sequence distribution, tacticity, branching, enchainment) and hence properties. In addition, because the emulsion polymerization takes place in an heterophase system and because the product is an aqueous dispersion, it is important to understand which performance characteristics are influended by the colloidal state, (i.e., particle size and size distribution) and which by the polymer infrastructure. 

The very high promise of reactions in heterophase systems is extended by K. Landfester who writes about the boom-topic miniemulsions. Miniemulsions are liquid/liquid dispersions with stable droplets with a size range between 30 nm[Pg.6]

The authors are indebted to the Shell Development Co. for supplying the tri-block copolymers, TR-41-1647, TR-41-1648 and TR-41-1649. H. Kawai and M. Shen also wish to thank the Japan Society for Promotion of Science, the Dreyfus Foundation, and the Office of Naval Research for support which has enabled them to cooperate in their research projects on heterophase systems, including this chapter. Finally, thanks are owed to the Editor of Rubber Chemistry Technology for permission to reproduce Figures 2 and 6-11 from the original paper (29). 

Rubber-resin heterophase systems are classified as (1) resin as the disperse phase, (2) rubber as the disperse phase, (3) grafted rubber latex particles as the disperse phase, and (4) filled graft rubber as the disperse phase. Adhesion mechanisms related to these systems are discussed. Special emphasis is made on the last two systems which involve grafting. The graft rubber isolated from the fourth system is characterized. The graft rubber is shown to function as a compatibilizer and as an adhesive or a coupling agent for the rubber-resin interface. 

Classification of Rubber-Resin Systems. Rubber-resin heterophase systems can be classified into four types according to the main constituent in the disperse phase ... 

Under defined conditions, the toughness is also driven by the content and spatial distribution of the -nucleating agent. The increase in fracture resistance is more pronounced in PP homopolymers than in random or rubber-modified copolymers. In the case of sequential copolymers, the molecular architecture inhibits a maximization of the amount of the /1-phase in heterophasic systems, the rubber phase mainly controls the fracture behavior. The performance of -nucleated grades has been explained in terms of smaller spherulitic size, lower packing density and favorable lamellar arrangement of the /3-modification (towards the cross-hatched structure of the non-nucleated resin) which induce a higher mobility of both crystalline and amorphous phases. 

To a first approximation, the system of rate equations describing processes in such heterophase systems can be written in the form (A = Zn, B = Se, B" = O)... 

Diffusion from the surface layer to the crystal bulk plays an important role in heterophase systems. It is the diffusion processes that determine in large part whether or not ZnO layers will grow and whether the ZnO/ZnSe(S,Te) heterojunction will have a sharp interface or the ZnO layer will grow via oxygen diffusion into the crystal bulk and will have a broad boundary. Solving Eqs. (8-11), one can determine, from the relationship between the generation rates of A and B vacancies, the quasi-heteroepitaxy parameters at which particular kinds of heterojunctions, conductivity types, and defect concentrations in ZnO and ZnSe(S, Te) layers can be obtained. 

This review covers the literature on the aggregation of (homo)polypeptide hybrid copolymers and copolypeptides in dilute solution, which was published up to June 2005 a recent review on amphiphiles consisting of peptide sequences is given elsewhere in [12]. It was a particular concern to give a comprehensive overview on secondary structure effects in the self-assembly of these copolymers. Briefly presented are also structures in concentrated solutions (lyotropic phases) and in heterophase systems (see also [14]). 

Combination of different polymers into heterophase systems represents a very attractive route towards new and tailor-made materials display-... 

Adolf et al [89] focused primarily on epoxy systems. They consider the key to the success of a constitutive model to be its choice of strain measure and the inclusion of free-energy-accelerated relaxations. The model only requires linear properties (i.e., properties that may be predictable by the methods developed in this book) for materials prior to their synthesis, since nonlinear behavior arises naturally from the formalism. Thermal properties and epoxy curing are also treated by their model. The authors have also attempted to treat failure by identifying a critical hydrostatic tension consistent with glassy failure. The model has been validated with a wide variety of types of material tests. The finite element simulations are performed in three dimensions. These authors have, thus far, done only a limited amount of preliminary work with heterophasic systems, but they report that the results were encouraging. 

The proper characterization and description of the interfaces between the phases is a key technical challenge to simulating the mechanical properties of heterophasic systems under large deformations. This challenge will be discussed now in the context of the conceptual framework of cohesive (bulk) and adhesive (interfacial) failure which was introduced in Section 7.C. 

The effect of structural memory in a wave field has been exsemplarily studied by the IR-spectroscopy method on films made from mixtures of butadiene-styrene and acrylic latex as models of polymeric membranes. The strengthening of the interphase interaction in heterophase systems that can cause change of their local and transmitting mobility has been observed. It has been shown, that the response of polymeric dispersed systems and compositions on influence of nonlinear vibrations proves their influence on deformation properties, like orientation phenomena in solid polymers (where Rebinder s effect can take place) that it is possible to consider as a way of polymer modifications, including the obtaining of nanicomposites, polymeric biocarriers, etc. 

Calorimetric data have shown that only half of the total water sorbed by elastin (about 0.6 g water / g dry protein) is really "bound", the remaining water being freezable ( 1). The volumetric data reported in the literature (15,16) refer therefore to an essentially heterophase system, so that the negative and very large coefficient of thermal expansion of the fully hydrated protein does not appear to be suitable for the Interpretation of the thermoelastic data and calculation of the... 

The purpose of our study was a rheological evaluation of the effect of composition on the properties of ABS resins in the molten state. Steady-state viscosity was determined over a wide range of temperatures and shear rates. The shear modulus in the molten state was determined by measurement of the diameter of the extrudate. ABS resins in the molten state behaved as an amorphous homophase polymer. The effect of the elastomer phase on the viscoelastic properties which characterize the behavior of the continuous matrix, i.e. monomer friction coefficient and molecular weight between entanglements (Me), was calculated by the application of the molecular theories. The significance of these properties in heterophase systems is discussed. 

Acrylonitrile-butadiene-styrene (ABS) resins are typical heterophase systems. 

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